Comparative Performance of Ethylene Glycol/Water and Propylene Glycol/Water Coolants in Automobile Radiators 960372

The heat transfer and hydraulic performance of the following coolants was examined in five automobile radiators in a wind tunnel:

• 100% Water
• 100% Propylene Glycol
• 70/30 Propylene Glycol/Water (Volume)
• 50/50 Propylene Glycol/Water (Volume)
• 70/30 Ethylene Glycol/Water (Volume)
• 50/50 Ethylene Glycol Water (Volume)

The results of these studies are presented to demonstrate the relative performance of these coolant mixtures in terms of heat transfer, coolant pressure drop and radiator effectiveness for a range of coolant flowrates and air flowrates.

It is concluded that the most effective of the coolants in transferring heat in the test radiators was water, followed by 50/50 ethylene glycol/water, 50/50 propylene glycol/water, 70/30 ethylene glycol/water, 70/30 propylene glycol and, finally, 100% propylene glycol.

The effect of replacing a 50/50 ethylene glycol/water coolant mixture with a 50/50 propylene glycol/water mixture in an automobile radiator depends upon the design of the radiator, the operating conditions and the amount of fouling. In situations where the air-side of the radiator contributes the majority of the resistance to heat transfer, the effect of changing coolants will be negligible and the coolant loop temperatures will increase by, approximately 0.5 - 1°C (1 - 2°F). In situations where the coolant provides the majority of the resistance to heat transfer the effect of changing coolants will be larger 2 - 3°C (4 - 6°F), but this would be an extreme case. The effect of an increase in the coolant return temperature upon the maximum metal temperature should be negligible, based upon the lower metal temperature that is achieved in nucleate boiling with 50/50 propylene glycol coolants compared to 50/50 ethylene glycol coolants, even with higher coolant temperatures [1].